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Anaesthesia > Clinically Anaesthetic Hazards & Scavenging > Flashcards

Clinically Anaesthetic Hazards & Scavenging Flashcards

1
Q

Anaesthetic breathing systems are used for what purpose?

A
  • to deliver oxygen &/or anesthetic agent and remove CO2
  • to prevent rebreathing of CO2
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2
Q

What are the three ways of classifying breathing systems?

A
  • with or without soda lime
  • Mapleson classification
  • Open, closed, semi-open/semi-closed
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3
Q

Soda lime systems are NOT

A

passive scavenging

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4
Q

What is the purpose of soda lime?

A

to absorb CO2 and allowing exhaled air to be re-utilised

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5
Q

soda lime produces

A

heat & water

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6
Q

soda lime should contain

A

an indicator to show when exhausted

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7
Q

What are some disadvantages of soda lime?

A
  • dehydrated when mixed w/ halogenated compounds and can produce carbon monoxide
  • compound A can be produced which is a nephrotoxic agent when using sevoflurane
  • color change is only temporary and can revert (must be read when still warm)
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8
Q

What breathing systems use soda lime?

A
  • circle
  • & technically to-and-fro (not used anymore)
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9
Q

What is the main feature of circle breathing systems?

A
  • unidirectional valves & soda lime canister so everything flows in 1 direction
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10
Q

if valve get sticky and doesn’t close properly in a circle system, what is the main consequence?

A

the patient will exhale CO2 to both sides and thus on the next inspiration will inhale CO2 from the inspiratory limb leading to massive CO2 inhalation very suddenly…

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11
Q

When the soda lime is exhausted, what does it do to CO2 and how does it affect vitals?

A
  • slow rebreathing of CO2 occurring
  • numbers change slowly
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12
Q

inhaled gas in a circle system consists of…

A

a mix of previously exhaled gas from which CO2 has been removed & variable fresh gas flow from a common gas outlet that includes oxygen and an anesthetic agent

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13
Q

In circle systems, FGF should be at what level when first establishing anesthetic depth?

A
  • it should be high to establish sufficient anesthetic concentrations in the system and anesthetic depth
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14
Q

if maintenance FGF is started at during anaesthesia, it is…

A

only enough to maintain sufficient oxygenation of P where the majority of air inhaled is exhaled air w/ no anesthetic agent and is only getting a tiny fraction of inhaled anesthetic agent

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15
Q

maintenance FGF must be adequate to replace

A

oxygen required for cellular metabolism, but only enough needed to maintain that lost per breath

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16
Q

What is the recommended initial FGF that should be used in a circle system?

A

100 ml/kg/min

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17
Q

When anesthetic depth is increased, what is the recommended FGF that should be used in a circle system?

A

100 ml/kg/min

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18
Q

How long should an animal on a circle system be given the recommended initial dose of FGF?

A

first 10-15 minutes of anaesthesia with the pop-off valve completely open and exhaled air completely leaves system

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19
Q

What is the recommended FGF in a circle system?

A

10-20 ml/kg/min
(however, most vaporizers req a minimum FGF of 500 ml/min for accuracy)

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20
Q

What 2 things in a circle system increase the system’s resistance?

A

unidirectional valves and soda lime

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21
Q

What size animal can be used on a circle system?

A

> 8-10 kg

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22
Q

When a circle system is used, how is the patient’s body temperature impacted?

A

the inspired gas is warmed and moistened so the patient is less hypothermic, but could lead to hyperthermia
can help keep P warm during maintenance phase

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23
Q

In a circle system, the concentration of inspired gas is NOT the same as

A

the vaporiser b/c there is a discrepancy between the vaporizer and the patient concentration thus it is lower in the patient than the vaporizer unless it is a really long procedure

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24
Q

concentration of inspired gas in a circle system CANNOT be

A

altered rapidly unless you increase FGF

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25
Q

What occurs in a circle system when the patient is breathing against increased resistance for long periods?

A

weak respiratory muscles so efficiency of ventilation decreases

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26
Q

When can a patient <8 kg receive a circle system?

A

If they need positive pressure ventilation

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27
Q

What are causes for rebreathing of CO2 in a circle system?

A

Exhausted soda lime
leaky unidirectional valves

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28
Q

What are the 3 types on non-rebreathing systems?

A

Ayre’s T-piece (& mods)
Bain (co-axial or parallel)
Lack (mini-lack)

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29
Q

What 2 pieces are missing from a non-rebreathing system that are present in a circle system?

A

No soda lime
No unidirectional valves

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30
Q

How do you rid a non-rebreathing system of CO2?

A

through high FGF

31
Q

During the expiratory phase of a non-rebreathing system, the high FGF must…

A

push all exhaled gases out of the system prior to the next inhalation

32
Q

What are the advantages of a non-rebreathing system in comparison with a circle system?

A
  • Concentration of inspired gas is the same as the vaporizer
  • concentration of inspired gas may be altered rapidly (w/I 1-2 breaths)
33
Q

What are the disadvantages of a non-rebreathing system in comparison with a circle system?

A
  • more costly to run (uses more O2 & vapor)
  • causes more atmospheric pollution
  • high gas flow contributes to P hypothermia
34
Q

What are the 4 main pieces of a Ayre’s T-piece?

A
  • fresh gas limb
  • reservoir limb
  • APL valve
  • reservoir bag
35
Q

How do you calculate the FGF for an Ayre’s T-piece?

A

2.5-3 x minute volume of the P (about 200 ml) = 500-600 ml/kg/min

36
Q

What patient size is recommended to use the Ayre’s T-piece?

A

P size <10 kg, with no lower weight limit

37
Q

Can you use IPPV w/ an Ayre’s T-piece?

A

Yes, highly recommended b/c more efficient and preserves FGF

38
Q

What are some causes for rebreathing of CO2 in an Ayre’s T-piece?

A
  • Insufficient FGF, not enough time to flush CO2 out properly
  • shortened expiratory phase (tachypnoeic)
  • excessive equipment dead space
39
Q

What are the three main pieces of a Bain non-rebreathing system?

A
  • fresh gas limb inside the reservoir limb
  • APL valve
  • Reservoir bag
40
Q

What should the FGF be for a Bain non-rebreathing system?

A

1.2-3 x Minute vol of P = 300-400 ml/kg/min

41
Q

A bain non-rebreathing system can be used in what size of patient?

A

> 10kg, up to 25 kg

42
Q

Can IPPV be used in Bain system?

A

Yes, recommended to decrease FGF

43
Q

What are causes of rebreathing of CO2 in the Bain system?

A
  • insufficient FGF
  • shortened expiratory pause
  • leak in the inner FGF limb–> enormous dead space causing rein halation of CO2
44
Q

What patient size can be used in a mini-lack system

A

3-10 kg

45
Q

Which non-rebreathing system is the most efficient?

A

Mini-lack

46
Q

What is the FGF recommended for use in mini-lack system?

A

0.8-1 x minute volume of p = 160-200 ml/kg/min

47
Q

Can IPPV be used with a mini-lack non-rebreathing system?

A

No!

48
Q

When does gas flow need to be altered when using systems w/o soda lime?

A
  • if the minute volume increases
  • if capnography is used
  • if IPPV is used
49
Q

When using a non-rebreathing system, do you need to alter FGF when you increase the depth of anaesthesia?

A

NO!

50
Q

The efficiency of breathing system is demonstrated by…

A

the rebreathing of CO2

51
Q

What is the equation for the minute volume of a patient?

A

RR x TV = MV

52
Q

if you are not using a capnograph, you should always use

A

a high level of FGF

53
Q

A scavenging system must be able to…

A

collect waste gases from the exhaust port of the anesthetic circuit & dispose of them outside the working environment

54
Q

What does the scavenging valve also known as?

A

pressure-relief valve
pop-off valve
spill valve
exhaust valve

55
Q

What is an adjustable pressure limiting valve?

A
  • special type of scavenging valve which prevents build-up of extremely high pressures
  • aka more sophisticated pop-off valve
56
Q

What is active scavenging?

A
  • exhaled gas is actively extracted from breathing system & expelled to the atmosphere
  • creates a vacuum & sucks out anesthetic & dumps outside
57
Q

What are the 3 components required in active scavenging?

A
  • scavenging valve of breathing system
  • connected to 22 mm tubing (in Europe)
  • attached to air-break/receiver which is connected to extractor fan (vacuum), through which the gas is vented to the atmosphere outside
58
Q

What is the main interface between the breathing system and the active disposal system that must protect the lung’s from excessive negative pressures in an active scavenging system?

A

Air brake

59
Q

What is passive scavenging?

A

No extractor is used to remove exhaled gas; driven solely but eh patient’s respiratory efforts

60
Q

in a passive scavenging system, it is important that there is

A

no massive resistance in the tubing

61
Q

When putting tubing out a window in a passive scavenging system, what is important to remember?

A
  • end of tubing must be at the same level as the scavenging valve or lower because anesthetic gases are heavier than air & will sink & not get out of the tubing
62
Q

When putting tubing out a window in a passive scavenging system, what is an important caution?

A
  • the tubes can get blocked
  • complete block = exhalation impossible
  • partial block = inhalation/exhalation difficult
63
Q

Aside from a tube out the window, what is another form of passive scavenging?

A

Activated charcoal

64
Q

How does activated charcoal passive scavenging work?

A

Exhaled air goes through scavenging (activated charcoal), and the halogenated gases (anesthetic) is absorbed into the charcoal and CO2 & O2 are exhaled into the room

65
Q

What is important to remember about activated charcoal?

A
  • absorbs halogenated gases, but does not render them inert & heating of the canister will release them
  • does NOT absorb N2O
66
Q

How do you know activated charcoal is exhausted?

A

It’s weight reaches the max weight on the canister which is heavier than it was when it was fresh

67
Q

How can you minimize workplace pollution w/ anesthetic agents?

A
  • check scavenging system
  • intubate P’s w/ cuffed ETT & inflate cuff
  • avoid face mask & induction chamber inductions
  • connect breathing system before turning on anesthetic vapors & turn gases off for any disconnections (Even short-term) & cap off to prevent gases escaping into the room
  • clear breathing system from anesthetic vapors w/ high O2 flow before disconnection (5 min)
  • fill vaporizers at end of day to minimize exposure
  • ventilate induction, operating, recovery areas
  • service equipment regularly
  • monitor theatre pollution at least q 2 yrs
  • leak test breathing system to prevent gases into room
68
Q

What are some short-term signs of exposure to high concentration of volatile agents?

A
  • headache
  • irritability
  • fatigue
  • nausea
  • drowsiness
  • difficulties w/ judgement & coordination
  • liver & kidney dz
69
Q

What are occupational exposure standards in IE?

A

Halothane: 10 ppm
Isoflurane: 50 ppm
N2O: 100 ppm
Sevoflurane: 60 ppm

70
Q

What are the hazards of ketamine injection?

A

hallucinations, convulsions, paralysis
long-term abuse –> brain atrophy/degeneration of white matter, decreased sociability, attention deficit, impaired memory recall/flashbacks; psychosis/ schizophrenia if predisposed

71
Q

what are the hazards of opioids?

A

abuse & addiction
resp depression

72
Q

What are the hazards of alpha-2 agonists?

A

CV alterations, resp depression

73
Q

What are hazards of Etrophine/ Immobilon?

A

severe resp depression, coma, death

Anaesthesia (24 decks)

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